1. Field of the Invention
The present invention relates to a clutch mechanism of an outboard motor for transmitting a driving force from a drive shaft or an input shaft rotationally driven by a drive system to an output shaft, and particularly relates to an improvement in the engagement condition between a forward gear and a reverse gear driven by the drive shaft, and a dog gear connected to the output shaft.
2. Description of the Related Art
In a conventional outboard motor 60 shown in FIG. 14, an engine (not shown) serves as a drive system above a casing 61, a drive shaft 62 is arranged vertically and driven by the engine, a clutch mechanism 64 is connected to a drive gear 63 at the lower end of the drive shaft62, and an output shaft 66 having a propeller 65 is connected to the clutch mechanism 64.
The clutch mechanism 64 has a forward gear 67 and a reverse gear 68 that are disposed for free rotation around the output shaft 66 and always driven to rotate in opposite directions by the drive gear 63 on the drive shaft 62, as well as a dog gear 69 provided around the output shaft 66 between the forward gear 67 and the reverse gear 67 to be rotationally immovable in the circumferential direction relative to the output shaft 66.
In the clutch mechanism 64, the dog gear 69 is engaged with either of the forward gear 67 or the reverse gear 68 by moving the dog gear 69 either toward the forward gear 67 or toward the reverse gear 68, wherein the driving force of one of the gears 67, 68 is transmitted to the output shaft 66, and the propeller 65 is thus rotated for forward or backward traveling.
In the clutch mechanism 64 of the outboard motor 60, as shown in FIGS. 15 and 16, engaging recesses 69a are provided on both sides of the dog gear 69 on the surfaces facing the forward gear 67 and the reverse gear 68, respectively, and engaging projections 67a, 68a are provided on the forward gear 67 and the reverse gear 68 on the areas facing the engaging recesses 69a. As the forward gear 67 or the reverse gear 68 is engaged, the engaging projections 67a, 68a are located within the engaging recesses 69a, with driving force transmitting surfaces 67b, 68b on the engaging projections 67a, 68a being abutted with driving force transmitting surfaces 69b in the engaging recesses 69a to transmit the driving force.
One of the well-known types of such a clutch mechanism for an outboard motor is described in JP-A-2005-48820, for instance. The noise emitted by the driving train is reduced by designing the engaging projections 67a, 68a and the engaging recesses 69a to have approximately the same lengths in the circumferential direction.
In the conventional clutch mechanism, however, the large output power of the engine sometimes causes breakage, cracks, deformations, and other damage to portions of the engaging projections 67a, 68a and the engaging recesses 69a when the forward gear 67 or the reverse gear 68 is engaged with the dog gear 69, or when the driving force is transmitted in the engaged state.